leetcode10

Combination Sum II

#coding=utf-8class Solution(object):    def combinationSum2(self, candidates, target):        """        :type candidates: List[int]        :type target: int        :rtype: List[List[int]]        """        res=[]        for i in range(len(candidates)):            self.solution(candidates,target-candidates[i],i,[candidates[i]],res)        return res    def solution(self,nums,target,index,path,res):        if target<0:            return        if target==0:            path.sort()            if path not in res:                res.append(path)            return        for i in range(index+1,len(nums)):            self.solution(nums,target-nums[i],i,path+[nums[i]],res)

First Missing Positive

。。。感谢python的强力

#coding=utf-8class Solution(object):    def firstMissingPositive(self, nums):        """        :type nums: List[int]        :rtype: int        """        i=1        while True:            if i not in nums:                return i            i+=1

正整数0位置应该是1，1位置是2，依次向下，所以当数组中出现的正数，把它对应的下标的值改为负，根据下标判断哪里是缺少的。

class Solution:    # @param A, a list of integers    # @return an integer    # @a very subtle solution    def firstMissingPositive(self, A):        n=len(A)        for i in range(n):            if A[i]<=0: A[i]=n+2        for i in range(n):            if abs(A[i])<=n:                curr=abs(A[i])-1                A[curr]=-abs(A[curr])        for i in range(n):            if A[i]>0: return i+1        return n+1

Trapping Rain Water

一个数组记录i左边最大的，再根据i右边最大的，计算i等接多少水

#coding=utf-8class Solution(object):    def trap(self, height):        """        :type height: List[int]        :rtype: int        """        if len(height)<3:            return 0        leftmax=[]        leftmax.append(0)        m=0        for i in range(0,len(height)-1):            if height[i]>m:                m=height[i]            leftmax.append(m)        maxright=height[-1]        res=0        print height        for i in range(len(height)-2,0,-1):            c=min(leftmax[i],maxright)-height[i]            if c>0:                res+=c            if height[i]>maxright:                maxright=height[i]        return res

Multiply Strings

因为要求不得使用任何内置的BigInteger库或直接将输入转换为整数。我这个复杂度有n^2，太高了

#coding=utf-8class Solution(object):    def multiply(self, num1, num2):        """        :type num1: str        :type num2: str        :rtype: str        """        temp=1        res=0        for i in num1[::-1]:            tmp=1            su=0            for j in num2[::-1]:                su+=int(i)*int(j)*tmp                tmp*=10            res+=su*temp            temp*=10        return str(res)